Field Mechanic - Cost: $950
The Medic for vehicles. The Mechanic is slow and unarmed, his purpose is to repair nearby friendly vehicles. Having a mechanic around means you can keep units in the battlefield instead of having to send them back to base for repair.

Chrono Tank - Cost: $2400
The Chronotank, as you will have no doubt guessed from the game, combines the assault capabilities of a tank, with the transport abilities of the Chronoshphere. It can go from anywhere, to anywhere, making an army of them lethal as they could appear behind the line of base defense and wreak havoc inside your base.

Demolition Truck - Cost: $700
Despite lacking the subtlety of the Chronotank, the Demo Truck is, nevertheless, just as deadly. It is effectively a small nuke on wheels. Send it into an incoming enemy attack to reduce it to dust, or send it in before your attack to take out defences and vehicular support.
Care is required when handling these however, as leaving one inside your own base can be costly as an enemy air strike may trigger it, taking out your entire base.